Therapeutic proteins or peptides in their native state or when recombinantly produced can be labile molecules exhibiting, inter alia, short periods of serum stability, serum half-life (i.e., circulatory half-life), or limited persistance in the body. Such molecules can also be extremely labile when formulated, such as when formulated in aqueous solutions.
In some instances, polyethylene glycol (PEG) conjugated to a proteinaceous molecule results in a longer-acting, sustained activity of the molecule. PEG attachment, however, can often substantially reduce or even destroy the protein's therapeutic activity. Therapeutic proteins and/or peptides have also been stabilized by fusion to certain proteins that are capable of extending serum half-life. For example, in some instances, therapeutic proteins fused to albumin, transferrin, and antibody fragments exhibit extended serum half-life when compared to the therapeutic protein in the unfused state. See U.S. Pat. No. 7,238,667 (particularly with respect to albumin conjugates), U.S. Pat. No. 7,176,278 (particularly with respect to transferrin conjugates), and U.S. Pat. No. 5,766,883, which are each hereby incorporated by reference in their entireties.
There remains a need in the art for more stable, longer acting, and/or effective proteinaceous molecules.